applet.avr: split CLI frontend off applet.program.avr. Other AVR programming interfaces generally expose the same features, and they should share the frontend.

applet: metaclass improvements for abstract applet base classes. * Make GlasgowAppletMeta inherit from ABCMeta. * Make build() and run() abstract methods. * Allow inheriting from GlasgowApplet without specifying a name. This results in an abstract applet, which is not registered in the applet database, and can be used to provide shared functions to other applets (usually, the interactive frontend).

database.microchip.avr: add ATmega{16,32}U4.

applet.memory.prom: encourage (sic) metastability during reads. This change is tested with Atmel AT29C flash and may or may not have any effect on other memories. In case of this Atmel flash, output buffers have parasitic feedback (likely through power supply) and will oscillate if encouraged, e.g. if OE is kept asserted, or if data transitions are maximized.

applet.memory.prom: s/histogram/popcount/ in commands.

applet.memory.prom: improved histogram ASCII art.

applet.memory.prom: fix DIV/0 in histogram for perfect flash.

applet.memory.prom: label histogram axes.

applet.memory.prom: add `atmel write` command. Also, make queueing actually work by escaping the RUN command if it happens to occur inside the buffered block.

applet.memory.prom: s/pass/sample/